British Prime Minister Theresa May once warned her fellow Conservatives of the perils of being known as the ‘nasty party.’ But after 100 days in office, she is in danger of going further, turning the United Kingdom into the nasty country.

In just a few months, May has launched attacks on “international elites” and decided to prioritise immigration controls over single-market access in negotiating the UK’s withdrawal from the European Union. At one point recently, companies faced the threat of being compelled to furnish a list of their foreign workers. And the 3.5 million European citizens who are settled in the UK were left to worry about whether May’s government would guarantee their residence rights.

It did not take long for the normalisation of nationalist rhetoric to affect the daily lives of Britain’s immigrant population. Indeed, hate crimes began to proliferate almost immediately after June’s Brexit referendum—even before May took power. Her government’s attitude seems to be a symptom, rather than a cause, of a broader nativist revival in Britain.

This revival has come on fairly quickly. As recently as the 2012 Olympic Games in London, the UK was showing a very different face to the world: welcoming, connected, and self-confident in its diversity. The current surge in identity politics seems to reflect a backlash against all that openness. In fact, Britain seems to be oscillating between inclusion and exclusion—and has been for four decades.

When Margaret Thatcher was Prime Minister in the 1980s, she promoted exclusion, defining British identity with reference to its enemies—and not just external foes, like the Soviet Union or the European Commission. There was no shortage of domestic villains: trade unions, miners, teachers, doctors, the BBC, ethnic minorities, the Scots, the Welsh, and Irish Catholics.

By the time John Major took over the premiership in 1990, there was a sense of national malaise, fueled by anguish about Europe and frustration with the declining prestige of British institutions. In 1995, opinion polls showed that only a minority of the country felt “British,” while many groups—namely young people, ethnic minorities, Londoners, Scots, and Welsh—felt poorly represented.

It was around that time that I, a precocious 23-year-old, became embroiled in the debate about national identity. In 1997, a few months after the election of Tony Blair and a few days after the death of Princess Diana, I wrote a report (PDF) arguing that, instead of mourning the death of the old narratives, we should celebrate the birth of new ones, reflecting pride in our past successes, while touting our creativity, diversity, and openness to business.

The point of my report, which was credited with spawning the political and media effort to rebrand the UK known as Cool Britannia, was to recognise Britain as a “silent revolutionary” that constantly renews itself, rather than basking in tradition. I was advocating a kind of progressive patriotism—one that was soon embraced by Britain’s political class, beginning with Blair himself.

To my surprise, when the Conservative Party started to renew itself under May’s predecessor, David Cameron, it focused on celebrating an inclusive national identity. Cameron and former London Mayor Boris Johnson, who now serves as foreign secretary, represented the modern, outward-looking, multiracial, multi-ethnic Britain that was broadcast to the world in the electrifying Olympic opening ceremony in 2012.

To be sure, within a couple of years, Cameron was calling for the Brexit referendum in a bid for votes, and Johnson was stepping up as a leader of the ‘Leave’ campaign. Nonetheless, they did not unravel the progress of the previous years.

A major opinion poll recently showed that almost a third of England’s people feel “very positive towards our multicultural society,” up from 24% in 2011. Meanwhile, the proportion of Britons who are most strongly hostile to immigration and a multicultural society has declined, from 13% to 8%. As TheEconomist’s Jeremy Cliffe argued in a 2015 paper, factors like rising racial diversity, a more educated citizenry, urbanisation, and increased variety in family structure seems to be giving rise to “an emerging cosmopolitan majority” in the UK.

As with any major social shift, diversity has its detractors. White, English, working-class men over the age of 55 feel particularly excluded from the progressive version of patriotism, and fear becoming a minority in their ‘own’ country. (According to data cited by Cliffe, the majority of the UK’s population will be non-white by 2070.) So they are revolting against cosmopolitanism—and May is playing to the crowd.

Some fear that this is the new normal. When May’s government first threatened to force companies to list foreign workers, I was dining with tech entrepreneurs from other EU countries who are settled in the UK. They joked darkly about being forced to wear blue stars on their clothes, speculating that the 1990s could one day be seen as an Anglo-Saxon version of Germany’s ill-fated Weimar period. That may be a stretch, but concerns that May’s decision to vacate the political centre could represent a long-term reversal of Britain’s political moderation are very real.

Fortunately, however, the long-term trend seems to be toward inclusion, even if the UK takes a couple of steps backward today. Even May herself, in her recent attack on cosmopolitanism, inadvertently celebrated Britain for precisely the achievements that its cosmopolitanism has enabled, from its outsize share of Nobel Prizes to the City of London’s financial clout.

Nonetheless, as the Brexit vote highlighted, Britain’s success is fragile. And the surge in hate crimes shows that the emerging cosmopolitan majority cannot simply sit back and wait for history to do its work. It must offer a new kind of politics that places a wedge between genuine fears and isolationism. It must show how Britain can reinvent its economy and state to deliver equitable growth, thereby regaining its agency in the world. And it must offer new ways to build solidarity and advance inclusion. Britain must not be allowed to become the nasty country.